Women experience significant disparities with regards to smoking cessation, and research has identified key factors underlying poor treatment response including differential response to smoking cessation medications. Despite this knowledge, findings have yet to translate into improved clinical outcomes for smoking cessation, and current guidelines provide little information on sex-based practices. One critical barrier for the translation to clinical practice is the lack of evidence from Phase-IV population-based studies. To date, evidence has exclusively emerged from Phase-III clinical trial data; sex differences in real-world effectiveness of stop smoking medications remain unknown. We will conduct a Phase-IV pharmacoepidemiologic study of sex differences in smoking cessation effectiveness in a U.S. nationally representative sample. [[[E-cigarette use during cessation attempts and associations with quitting will also be examined.]]] Our study will be a secondary analysis of the first wave of the Population Assessment of Tobacco and Health (PATH) study (scheduled to be released in the Fall of 2015), which was initiated and funded by NIDA and the FDA. The study's large sample size (~59,000) and its inclusion of information on medication/e-cigarette use during attempts to stop smoking will present a unique and unprecedented opportunity to address the study's aims. The project will also serve as the foundation for an R01 application for subsequent analyses of longitudinal waves of PATH data. [[[Our primary aim will be to examine sex differences in the real world comparative effectiveness of smoking cessation medications, using both regression and propensity score approaches, and following published guidelines for medication effectiveness studies using secondary data sources.]]] Data from current and former smokers who attempted to quit smoking (either successfully or unsuccessfully) at least once during the 12 months prior to their interview (n~8,215; 4,240 men and 3,975 women) will be analyzed. The investigation will examine the comparative effectiveness of the following medications: nicotine replacement therapy (the patch, oral NRT, nasal spray), varenicline/Chantix, and bupropion/Wellbutrin/Zyban. We will explore whether sex differences in medication effectiveness are moderated by education level, annual income, race/ethnicity, nicotine dependence level, and mental health. [[[We will also explore sex differences in associations between use of e-cigarettes during cessation attempts and likelihood of successful cessation.]]] This study addresses the National Institute on Drug Abuse's (NIDA) call for projects that assess the differential effectiveness of current drug abuse treatments in males and females (PA-14-037: Women & Sex/Gender Differences in Drug and Alcohol/Dependence).